A piezoelectric element is an element in which a piezoelectric film, having an electromechanical transducing function, is sandwiched by two electrodes. The piezoelectric film is made of crystallized piezoelectric ceramics.
Conventionally, a so-called sol-gel method has been known as a manufacturing method of the piezoelectric element. Specifically, a sol of an organometallic compound is applied on a substrate in which a lower electrode is formed, and then the sol is dried and degreased to form a precursor film of a piezoelectric layer. After the steps of application, drying and degreasing of the sol is carried out predetermined times, the sol is subject to heat treatment at high temperature to be crystallized. In order to increase the thickness of the layer, the steps of application, drying and degreasing, as well as the step of crystallizing the sol are further carried out on the crystallized piezoelectric layer repeatedly.
A degreasing method using a tray dryer or a hot plate is known as a method of degreasing the above mentioned sol of the organometallic compound.
Further, this type of piezoelectric element is applied to a liquid jet head such as an ink-jet recording head. In the ink-jet recording head, a vibration plate constructs a part of each pressure generating chamber which communicates with a nozzle orifice for ejecting ink, and the vibration plate is deformed by the piezoelectric element to pressurize ink within the pressure generating chamber and thereby the ink droplets are ejected from the nozzle orifice. There are two types of ink-jet recording heads which are in practical use: the ink-jet recording head using a piezoelectric actuator in a longitudinal vibration mode where the actuator stretches and shrinks in an axis direction of the piezoelectric element; and the ink-jet recording head in a flexural vibration mode. The ink-jet recording head in the flexural vibration mode is typified by a known ink-jet recording head in which the piezoelectric elements are formed in the following manner: a uniform piezoelectric layer is formed over the entire surface of the vibration plate by a deposition technology; and the piezoelectric layer thus obtained is cut using a lithography method into pieces, each having a shape corresponding to each pressure generating chamber so that the piezoelectric elements are formed separately for the respective pressure generating chambers.
There is an example of the ink-jet recording head having the aforementioned piezoelectric element in the flexure vibration mode, which is disclosed in Japanese Patent Laid-Open Publication No. 2000-326503. In this ink-jet recording head, a lower electrode which constitutes the piezoelectric element is patterned in a region facing the pressure generating chamber, thus suppressing initial flexure of the vibration plate and increasing an amount of displacement of the vibration plate due to drive of the piezoelectric element.
In the conventional degreasing step in manufacturing the piezoelectric element, nucleuses of piezoelectric crystals in the precursor of the piezoelectric film has not been easily formed. Therefore, it has been difficult to obtain desired crystals when the precursor is crystallized. Moreover, degreasing conditions have varied due to, for example, variations in a rate of temperature increase depending on a position within the wafer surface. This could result in variations in crystal orientations and piezoelectric properties.
Moreover, when forming the piezoelectric film on the lower electrode which is patterned as mentioned earlier, a problem arises that portions of the piezoelectric film formed to cover edges of the lower electrode and other portion of the same formed on the outer sides of the lower electrode have poor film qualities, and thereby a drive reliability of the piezoelectric element is degraded. In other words, the piezoelectric film on the lower electrode and the same on the outer sides of the lower electrode have different properties of crystals and the like. Thus, the piezoelectric layer is substantially discontinuous in the vicinities of edges of the lower electrode thereby causing breakage such as a crack in the piezoelectric film when a voltage is applied thereto. This breakage easily happens particularly in the piezoelectric film in the region corresponding to the edges of the lower electrode in a longitudinal direction thereof.